This invention relates to automotive tire pressure sensors. More particularly, this invention relates to a method and system for monitoring internal tire pressure of vehicles using an externally mounted sensor.
Tire pressure sensor systems are known and are commonly used to monitor the internal air pressure in individual pneumatic tires of a vehicle and to provide a warning signal to the driver whenever the internal air pressure in one or more of the vehicle tires is dangerously low or high. The warning signal is typically generated by an r.f. signal generator controlled by a microprocessor connected to the tire pressure sensor whenever the internal tire pressure measured by the sensor lies outside a predetermined normal operating range. This r.f. signal is transmitted to a vehicle-mounted receiver, which uses the warning signal to alert the driver either visually (by activating a warning lamp or display) or audibly (by activating an audible alarm) or both.
Known tire pressure systems typically employ one of two basic design configurations. The first type of design configuration employs an internal arrangement in which all components comprising the signal transmitting portions of the tire pressure sensor system are positioned within the tire casing. In a typical installation of this type, the pressure sensor, r.f. generator, the microprocessor, and the D.C. battery power source are physically installed inside the pneumatic tire casing prior to inflation of the tire, usually by attaching these components to an inner surface of the wheel. Design configurations of this first type suffer from several disadvantages. Firstly, the installation of the system components within the tire casing is not simple, requires careful attention to the component location and mounting, and increases the manufacturing cost of the entire automobile. In addition, many vehicles use steel-belted tires, which interact in a detrimental manner with the r.f. signals generated internally of the tire. Further, when the battery or one of the other system components fails, replacement of the defective component requires that the affected tire be removed from the wheel before replacement can be done, which is costly and time consuming.
The second type of basic design configuration used for current tire pressure sensor systems employs components which are mounted in a cap which is threadably attached to the exposed outer end of the valve stem of the tire. While this design arrangement avoids the disadvantages noted above associated with internally mounted tire pressure monitoring systems, it introduces the following additional disadvantages. Firstly, because the pressure monitoring system is carried by the externally-protruding valve stem, the acceleration force produced by the rotating wheel and tire, which can reach a magnitude of 200 g., can severely impair the accuracy of the sensor system. In addition, the system components can easily be inadvertently lost or stolen.
Efforts to provide a simple yet accurate and durable tire pressure monitoring system devoid of the above-noted disadvantages have not been successful to date.